It could oftentimes be unstable and not properly tested, lacking any changelogs, but eventually evolving into alphas, betas, release candidates, and finally stable releases.
Update: Confirmed working on both Sensation and T-Mobile Sensation 4G.
Have an HTC Sensation or T-Mobile Sensation 4G? Your day may have just gotten a little better - CyanogenMod 9 (Android 4.0) nightlies have officially arrived. While we're not 100% sure this ROM actually will work on the T-Mobile version of the Sensation, this thread suggests it's likely possible. That doesn't mean it's particularly easy, though - so be sure you know what you're doing before you go flashing away.
Hit up CyanogenMod downloads now to get the ROM.